CD105 or Endoglin or GP160 is a Type I transmembrane protein, which is highly expressed on human vascular endothelial cells. It exists as an O- and N-glycosylated homodimer. Up-regulation of endoglin expression has been demonstrated in tumor vasculature and proliferating cells, suggesting that it is a proliferation-associated endothelial cell marker. CD105 binds to TGF-Beta1 and Beta3 with high affinity but not TGF-Beta2.